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Rev Sci Instrum. 1978 Jun;49(6):785.

Automatic NMR field-frequency lock-pulsed phase locked loop approach.

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Institut d'Electronique Fondamentale, Laboratoire associe au CNRS, Universite Paris-Sud, 91405 Orsay, FranceLaboratoire de Chimie Organique Structurale, Universite Paris Sud, 91405 Orsay, France.


A self-contained deuterium frequency-field lock scheme for a high-resolution NMR spectrometer is described. It is based on phase locked loop techniques in which the free induction decay signal behaves as a voltage-controlled oscillator. By pulsing the spins at an offset frequency of a few hundred hertz and using a digital phase-frequency discriminator this method not only eliminates the usual phase, rf power, offset adjustments needed in conventional lock systems but also possesses the automatic pull-in characteristics that dispense with the use of field sweeps to locate the NMR line prior to closure of the lock loop.


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